Beam therapy collimating unit



April 13, 1954 D. T. GREEN ET Al.

BEAM THERAPY COLLIMATING UNIT 4 Sheets-Sheet l Filed Feb. 5, 1952 April 13y 1954 D. T. GREEN ET A1. 2,675,486

BEAM THERAPY COLLIMATING UNIT Filed Feb. 5, 1952 '4'Sheets-5heet 2- F1 Q 5 C42/CFM@ scarf /vccoz/vk BY ATT ,QA/EVS April 13, 1954 D. T. GREEN ETAL 2,675,486

BEAM THERAPY COLLIMATING UNIT Filed Feb. s. 1952 Y 4 sheets-sneer s April 13, 1954 D, T, GREEN ET AL 2,675,486

BEAM THERAPY COLLIMATING UNIT l Filed Feb. 5. 1.952 4 Sheets--5heet 4 ATTO NEYS Patented Apr. 13, w1954 BEAM THERAPY COLLIIMATING UNIT Donald T. Green and Clifford S. McColm, Ottawa,

Ontario, Canada, assignors, by mesne assignments, to Atomic Energy of Canada, Limited, Ottawa, Ontario, Canada, a corporation of Canada Application February 5, 1952, Serial No. 270,054

Claims priority, application Canada December 8, 1951 .This invention is concerned with a collimator to denne a beam-of radiation.

The primary application of this device is to the collimation of the radiation from a radio active source of Co60 to be used for therapeutic purposes but it could be used vfor other isotopes emitting high energy gamma radiation or for high voltage X radiation. The same principles could also-be applied to collimators for low energy gamma or X radiation in which case the thickness of material necessary to denne a beam of high energy radiation could be considerably reduced.

An ,object of the present invention is to provide a collimator, for radiation, the aperture of which can be innitely varied through a wide range of square and rectangular shapes.

` A further object is to provide a collimator in whichl the aperture is defined by blocks disposed in a single plane and movable only in one plane.

Another object is to provide a convenient means for varying the distance between the source of radiation and the blocks which define the aperture 'of the collimator, thereby enabling a constant distance from aperture to skin to be maintained for a range of treatment distances (source to skin distances).I This is of importance as it is undesirable for the skin to be too close to the blocks as the skin may then be subject to secondary radiation emitted by the blocks, and on the other hand too great a distance will result in a i blurred and poorly dened beam.

In accordance with this invention the distance betweenv the source of radiation and the blocks is'varied by providing a cylindrical upper shell telescoping with a cylindrical lower shell within which are disposed the blocks which define the aperture for the 'emission of the beam. The upper and` lower shells are telescoped by means of a series of Screws parallel to the axis of the shells and spaced about the periphery of one shell and secured thereto in a manner which prevents axial rotation and movement in a direction parallel to these axes. A series of nuts co-operating with these screws are rotatably supported by the other shell so that the nuts may be turned in one directionto extend the shell and may be rotated in the other direction to close up the shell. A series of sprockets corresponding to said nuts are operably connected thereto so that the rotation of each sprocket causes rotation of the .Y

corresponding nut. A continuous sprocket chain is carried by the sprockets so that all of the sprockets will rotate simultaneously. Means are provided for rotating one of the sprockets whereby allofthe nut's'wll be rotated.

:'L' mounted on the base plate.

13 Claims. (Cl. Z50-105) The beam of radiation is deiined by blocks movable in a unitary plane which is substantially perpendicular to the axis of the beam of radiation. These blocks comprise two pairs of opposed parallel blocks, the blocks of one pair being at right angles to the blocks of the other pair. The inner face of each block is in abutment with and slidable along the end of one of the blocks in the other pair and its end is in abutment with and slidable along the inner face of the other of the blocks in the other pair. Means are provided for maintaining the blocks in abutment as aforesaid and mounting means is provided for the blocks which permit the movement of each of the blocks within the unitary plane in a direction parallel to the ends of the block and also in a direction perpendicular thereto. Means are also provided for increasing or decreasing the distance between one of said pairs of blocks and means for increasing or decreasing the distance between the other of said pairs of blocks. As the distance between one of the pairs of blocks s increased or decreased the other blocks will be moved in opposite directionsl along parallel paths. Hence a square or rectangular aperture will at all times be defined by the two pairs of blocks.

Conning the blocks to a unitary plane is considered to be of great importance. If two or more planes were used the total thickness of the defining portion would be twice as great as in accordance with the present invention and the total weight would also be somewhat greater. In addition the distance to the skin from one pair of defining blocks would be diiierentthan for the other pair, thus losing some denition of the beam for any given distance. Further, the centre of gravity of the defining system would be further from the source for a system capable of a certain minimum placement from the source, and thus the entire device would be more difficult to rotate about a horizontal axis.

In the drawings which illustrate the preferred embodiment of this invention:

Fig. 1 is an elevation view partly in section of the collimator.

Fig. 2 is a plan view partly broken away of the collimator shown in Fig. 1.

Fig. 3 is a plan view showing a different position of the blocks from that illustrated in Fig. 2.

Fig. i is an elevation view partly in section corresponding to Fig. 3. A

Fig. 5 is a sectional view illustrating the base plate-assembly.' 'A v' Fig. 6 is a perspective view showing the blocks Fig. 7 is a detailed View of the lower cam plate. Fig. 8 is a view illustrating the general assembly of the collimator and the source of radiation. In the drawings in which the same numerals indicate similar parts a cylindrical upper shell I slidably engages a cylindrical lower shell 2 so that the lower shell 2 will telescope within upper shell I. Four screws of which 3 and 4 are illustrated are symmetrically disposed around the periphery of shell I, the screws being parallel to the axis of shell I and being within the shell. The screws are anchored to an inwardly directed flange 5 at the top of shell I in a manner which prevents axial rotation and. movementv in a direction parallel to these axes. At the upper portion of shell 2 there is an inwardly directed flange 6 within which is journalled a series of lnuts corresponding to each of the four screws, nuts 1 and 8 being illustrated. Ball bearings 9 facilitate the rotation of these nuts. A series of sprockets corresponding to the nuts, of which I and I I are illustrated, are rigidly connected with or integral with the nuts so that rotation of the sprockets rotates their corresponding nuts. An additional needle bearing I2 engaging a shaft I3 which downwardly depends from the sprocket can be provided to give additional support to the nut sprocket assembly. Shaft I3 is preferably hollow. A sprocket chain I4 encircles the four sprockets so that rotation of one sprocket causes all four sprockets to rotate simultaneously in the same direction. Idler sprocket 20, adjustable in groove 2I, provides for the adjustment of chain I4. A vertical scale may be provided on the lower shell 2 which is read oil from the lower edge of the upper shell I. This scale will show the correct relative position of the shells for any treatment distance within the useful range. A cylindrical tube I5 replaces bearing I2 and shaft I3 in one of the nut spocket assemblies. Tube I5 is rigidly secured to sprocket I0 so that rotation of tube I5 causes rotation of sprocket I0 and nut 1. A shaft I6 is inwardly directed with respect to shell 2 perpendicular to the axis of tube I5. A handle I1 exterior to shell 2 turns shaft I6. A helical gear I8 mounted on shaft I6 meshes with a corresponding gear piece. I9 at the bottom end of Shaft I5 so that shaft I5 will rotater when the handle I1 is turned. Shaft I6 is journalled in a bearing 22 which is mounted on base plate 23. The screws are permitted slight, angular and lateral displacement to prevent binding when the nuts are close to the heads of the screws.

Plates 24, 25, 26 and 21 are mounted on base plate 23 between rollers 28 which engage grooves 23 in the side edges of plates 24, 25, 26 and 21. These rollers permit plates 24, 25, 26 and 21 to move inwardly or outwardly with respect to base plate 23 but prevent lateral movement. Addi tional rollers 30 are mounted on plates 24, 25, 26 and 21. Rollers 30 engage grooves 3I in. the side edges of plate 32. There are four plates 32 corresponding to each of plates 24, 25, 26 and 21, and plates 32 are mounted between rollers 30 so that each of ,plates 32 is capable of movement relative to its corresponding plate 24, 25, 26 or 21 in a direction perpendicular tothe direction of movement of its corresponding plate. It will be evident that the combined effect of mounting plates 24, 25, 26 and 21 between rollers 29, and plates 32 between rollers 30 is to enable plates 32 to assume a variety of position in a unitary planer parallel to base plate 23.

Blocks as. sa, as and 36./are rigidly; mounted 0n each of plates 32 and are movable with plates 32. The blocks are arranged with their longest dimension in the direction or movement Vof plate 32 with respect to plates 24, 25,. 26 or21. The inner surface 31 of block 33 is partly in abutment with the end 36 of block 34 adjacent to one end of block 33 and the other end of block 33, namely 39, is` partly or completely in abutment with .the inner face 40 of block 36. Similarly one endof-block 34 is in abutment with the inner face 31, of block-.33,.and at the other end of block 34'there1 is an` abutment between the inner face of block 34 and the end of block 35. One end of block 35 is in` abutment with the inner face of block 34 and at the other end of block 35 there is-abutmentfwith the end of block 36. lOne end orblock 36 is in abutment with inner face of block 35 and at the other end of block 36 there is abutment between the inner face 39 of block l36 and the end of block-33.

It will be'appreciated from the` foregoing;Y that ii; a pair. of parallel opposed blocks' 33 land 36.; are moved inwardly towards each other'v from an initial position ad'iacentto the periphery of base plate 23, the `inward movement of block 33will f cause block 34 to move in the'same direction as block 33, the plate 32 upon which block 3'4 .is mounted sliding between. its rollers 30'.. Similarly the inwardmovement Voi! blocks 35 will cause block 36 to move in the same directioxras block 3,5 the inner face 4U of block36 sliding with respect to the abutting end 39 of blocky 33 and the plate 32. uponl which block.36.is mounted moving between its rollers.30. A rectangular space will thereby be defined by blocks` 33 34,35 and 36. Similarly if' blocks 34 and which are paralleland. in opposed positionwith, respect to each other are moved. inwardly, blocks 33 and35 will move in oppositeparallel directions, block 33 moving in the same .direction as block. 36 .and

block 35 moving in .thesame direction..as, block 34. If blocks` 33 and.35` are` broughttogether to the same .extent as blocks 3.4 and 3.6 a square spacev will be enclosed by the blocks.

Plates 4I,.42,v 43. and 44 are mounted ont-he inner faces. of blocks 3334, 35 and 36 respectively. These plates extend the fulllength of their corresponding .blocks and. have portions such as 45 whichextend slightly above the upper surfaces of the corresponding blocks. Facing plates 4I, 42, 43 `and:44.-also have downwardly extending portionsri46 which extend beneath the lower surfaces of` the corresponding blocks adistance which is approximately equal to the. height of the blocks. Thesey downward extensions-enable suitable deiinition for the. beam to beg-pro-` vided whilst keeping the heavy mass of the block as close as possble'tc` thesource and' as far-as possible from the: patient. This means'that the treatment unit iseasier to tilt, due to their being a lower moment about the horizontal axis, the 5' yheavy blocks can be smal-ler in size', andi there is less scattered radiation delivered' tothe `patients skin. The inner surfaces of p1ates-=4Ii,'42, 43 and 44 have longitudinally extending grooves 41,

which correspond to raised portions 48 in the f abutting end of thelblock and they facing. plate in contact with that inner face, in order that there may-be no direct downward path between abutting blocks for the'eseape'of radiation. Thism constructionprevents theiescapefof-radiation and enables rollersito lbe included vwhichughna'. rolling rather than slidingl frictionrbetweenvtherblocks.. A strap: 49.*is' mountedlon each-of blocks-133,.- 34.,V 35 and 36 at the endrof-therblodtfwhieh-ienot in abutment with the inner face 'o1' another block. At the abutting end of the block a plate 59 is located on the upper surface of the block adjacent to the end of the block. Spaced upwardly extending studs 5| and 52 are diagonally disposed on block 59. A clamping piece 53 is placed with its shank portion 54 between studs 5| and 52, and its head portion 55 extending over the facing plate 4|, 42, 43 or 44 of the adjacent block. A roller 56 is mounted on the lower surface of head portion 55 and moves along the outer surface of extension 45. A tension spring 51 is connected between strap 49 and the end of shank 54 and this urges roller 56 against the outer surface of extension 45 thereby tending to keep the end of one block in close abutment with the inner face of a second block while permitting the inner face of the second block to slide relatively to the abutting end of the first block. A roller 58 mounted in an indentation 59 in the end of extension 45 bears against the inner face of extension 45 in the adjacent block and reduces the friction when the inner face of one block slides with respect to the abutting end of another block. Similarly at the bottom of downward extension 46 a roller 60 is urged against the outer surface of the downward extension 46 of an adjacent block by a spring 6| connected between clamp 62 and a strap 63.

Cam followers 64 are mounted beneath each of plates 24 and 26 on supports 65 which are secured to plates 24 or 26. Apertures 66 in plates 24 or 26 provide access to bolts 61 which secure -cam followers 64. Cam followers 64 engage arcuate oppositely disposed cam grooves 6-9 in cam plate 69. Cam plate 69 is in the form of an annular ring with inwardly directed fins 10 in the upper surfaces of which are cam grooves 63. A groove 1| runs around the outer edge of cam plate 59 to provide a race for balls 12 which are retained in an annular groove 13 in a cylindrical ange 14 which downwardly depends from the edges of plate 23. A handle 15 is attached to cam plate 69 and this moves through a slot 16 in flange 14. A scale 11 mounted on flange 14 enables the extent to which handle 15 has been moved to be measured. It will be appreciated that movement of handle 15 in a clockwise direction causes cam followers 64 to ride up to the inner end 18 of cam groove 68, this moves plates 24 and 26 inwardly and consequently moves blocks 33 and 35 towards each other. Similarly movement of handle 15 in an anti-clockwise direction increases the distance between blocks 33 and 35.

Cam followers 19 are mounted beneath plates and 21 in a similar manner on supports I8 which bring cam followers 19 into a position beneath cam plates 69 and radially inwardly from theannular edge of cam plate 69 so that there will be no interference between cam followers 19 and upper cam plate 69, cam followers 19 engage cam grooves 8l in a cam plate 82. The annular edge of cam plate 82 is wider than the annular edge of cam plate 69 and the fins and cam grooves in cam plate 82 are inwardly disposed with respect to the corresponding members in cam plate 69. The edge of cam plate 82 is grooved as at 83 to provide a face for balls 34 which are carried by an annular groove 95 in cylindrical iange 14. A handle 86 is secured to cam plate 82 and this moves in a slot 85a in flange 14 to enable the inward and outward movement of blocks 34 and 36 to be controlled in the same manner as that described for blocks 33 and 35.

Base plate 23 has a square central aperture 81 to permit free movement of the downwardly ex' tending portion 46 of the facing plates and to provide an opening for the emission of the beam of radiation. A rectangular indentation 88 in base plate 23 permits lateral movement of the downward extension 46 of facing plate 44 and indentations 89, 98 and 9| are provided for a similar purpose with respect to the downward extensions of facing plates 4|, 42, and 43 respectively. n An inwardly directed slot 92 in base plate 23 permits inward and outward movement of cam followers 64 and similarly slots are provided to allow inward and outward movement of the other cam followers. The downwardly extending portion 46 of the facing plates may require slotting as at 93 to prevent interference with the cam plates.

Figure 8 illustrates the general arrangement of the collimator and the source of radiation. It will be seen that source of radiation 94 outlet port 95, beam limiting aperture 96 and the collimator indicated generally at 91 are in alignment. The source may be positioned by means of a sliding tray between absorptive lead housings 98 and 99. A conical shaped outlet port 95 in lead housing 99 defines a beam of radiation which is restricted by beam limiting aperture 96. Outlet port may be closed off by the insertion of mercury.

Source 94, outlet port 95, aperture 96, housing 99, are mounted upon upper shell The collimator 91 is mounted in lower housing 2 which telescopes with upper housing in the manner described. v

It Will be appreciated from the foregoing that a device in accordance with the present invention will enable a xed distance to be preserved between the defining blocks and the patient for different distances from the source to the patient and will achieve the various other objects of this invention.

We claim:

l. In a collimator for defining a beam of radiation a lower shell telescoping with an upper shell, means for defining the beam disposed within the lower shell, means for telescoping the upper and lower shells comprising a series of screws attached to one shell and parallel to the direction of telescoping, a series of nuts engaging said screws said nuts being journalled in bearings in the other shell and means for simultaneously rotating all of said nuts whereby the shells will be telescoped together.

2. In a collimator for defining a beam of radiation an upper shell telescoping with a lower shell, means for defining the beam disposed within the lower shell, means for telescoping the upper and lower shells comprising a series of screws parallel to the direction of telescoping spaced about the periphery of one shell and secured to that shell ga series of nuts engaging said screws said nuts being journalled in bearings in the other shell and means for rotating all of said nuts simultaneously whereby the upper and lower shells will be telescoped together.

3. A device as in claim 2, in which the means for rotating the nuts simultaneously comprises a series of sprockets corresponding to the nuts and operably connected thereto, a continuous `sprocket chain carried by said sprockets and means for rotating one of said sprockets.

. 4. In a collimator for defining a beam of radialtion a cylindrical upper shell telescoping with a cylindrical lower shell, means disposed within the lower shell to dene a beam of radiation,

means for telescoping the upper and lower shells comprising a series of screws parallel to the axis of said shells spaced about the periphery of one shell and secured to that shell, a series of nuts co-operating with said screws and rotatably supported by the other shell, a series of sprockets corresponding to said nuts and operably connected thereto, a continuous sprocket chain carried by said sprockets and means for rotating one of said sprockets.

5. In a collimator for defining a beam of radiation a cylindrical upper shell telescoping with a coaxial cylindrical lower shell, blocks disposed within the lower shell and movable in a plane transverse to the axis of the shell to define an aperture for the emission of the beam of radiation, means for telescoping the upper and lower shells comprising a series of screws parallel to the axis of the shells spaced about the periphery of one shell and secured to that shell a series of nuts co-operating with said screws and rotatably supported by the other shells, a series of Sprockets corresponding to said nuts, and operably connected thereto, a continuous sprocket chain carried by said sprockets and means for rotating one of said sprockets.

6. In a collimator for deiining a beam of radiation a cylindrical upper shell telescoping with a coaxial cylindrical lower shell, blocks movable in a` imitanr plane substantially perpendicular to the axis of the beam of radiation to define an aperture for the emission of the beam, said blocks comprising two pairs of opposed parallel blocks, the blocks of one pair being at right angles to the blocks of the other pair, each block having its inner face in abutment with and slidable along the end of one of the blocks in the other pair and having its end in abutment with and slidable along the inner face of the other of the blocks in the other pair, means for maintaining the blocks in abutment as aforesaid, supporting means for the blocks permitting movement of each block within said unitary plane in a direction parallel to the axis of said block and in a direction perpendicular thereto, means for increasing or decreasing the distance between one of said pairs of blocks and means for increasing or decreasing the distance between the other of said pairs of blocks, means for telescoping the upper and lower shells comprising a series of screws parallel to the axis of the shells spaced about the periphery of one shell and secured to that shell, a series of nuts co-operating with said screws and rotatably supported by the other shell, a series of sprockets corresponding to said nuts and operably connected thereto, a continuous sprocket chain carried by said sprockets and means for rotating one of said sprockets.

7. In a collimator for deiining a beam of radiation, blocks movable in a unitary plane substantially perpendicular to the axis of the beam of radiation to define an aperture for the emission of the beam, said blocks comprising two pairs of blocks, the blocks of each pair being parallel to each other and at right angles to the blocks of the other pair, each block having its inner face in abutment with and slidable along the end of one of the blocks in the other pair and having its end in abutment with and slidable along the inner face of the other of the blocks in the other pair, means for maintaining the blocks in abutment as aforesaid, mounting means for said blocks permitting movement of each of said blocks within said unitary plane in a direction parallel to the axis of said blocks and in a direction perpendicular thereto, means for increasing or decreasing the distance between one of the said pairs of blocks and means for increasing or decreasing the distance between the other of said pairs of blocks.

8. A device as in claim 7 in which the mounting means for said blocks to permit movement of said blocks within said unitary plane in a direction parallel to the axis of said blocks and in a direction perpendicular thereto comprises for a plate on each of which one of said blocks is mounted in a manner which permits relative movement between said block and said plate only in a direction parallel to the axis of the block. each of said plates being mounted on a base in a manner which permits movement only in a direction perpendicular to the axis of said block.

9. A device as in claim 8 in which the means for increasing or decreasing the distance between said pairs of blocks comprises cam followers mounted beneath the plates, a cam plate for moving the cam followers associated with one pair of blocks inwardly or outwardly to decrease or increase the distance between that pair of blocks, and a second cam plate for moving the pair of cam followers associated with the other pair of blocks inwardly or outwardly to decrease or increase the distance between the other of said pairs of blocks.

10. A device as in claim 9 in which the cam plates are in the form of an annular ring having diametrically opposite inwardly directed iins and arcuate cam grooves in said ns.

1l. A device as in claim 7 in which each of the means for maintaining the blocks in abutment comprises a clamp extending beyond the end of a block which is in abutment with the inner face of another block and engaging an upward extension along the inner face of said other block, said clamp having a shank portion slidable between upwardly extending studs mounted on the first mentioned block and the clamp being connected to a tension spring longitudinally disposed with respect to the iirst mentioned block.

l2. A device as in claim 7 in which the inner face of each of said blocks comprises a facing plate having a portion extending downwardly below the block.

13. A device as in claim 7 in which each of the inner faces of the blocks have longitudinally extending grooves which correspond with raised portions at the end of the block which co-operates with said face.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,506,658 Nowak Aug. 26, 1924 1,600,867 Coolidge Sept. 21, 1926 1,909,118 Raab May 16, 1933 2,076,240 Levy Apr. 6, 1937 2,090,270 Swanson Aug. 17, 1937 2,412,662 Watson Dec. 17, 1946 2,542,196 Haupt Feb. 20, 1951 

